import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.image.MemoryImageSource;
import java.util.Random;

import javax.swing.JDialog;
import javax.swing.JPanel;
import javax.swing.Timer;

@SuppressWarnings("serial")
public class Rain extends JDialog implements ActionListener {

	private Random random = new Random();
	private Dimension screenSize;
	private JPanel graphicsPanel;
	// 行高,列宽
	private final static int gap = 20;
	// 存放雨点顶部的位置信息(marginTop)
	private int[] posArr;
	// 行数
	private int lines;
	// 列数
	private int columns;

	public Rain() {
		initComponents();
	}

	private void initComponents() {
		setLayout(new BorderLayout());
		graphicsPanel = new GraphicsPanel();
		add(graphicsPanel, BorderLayout.CENTER);
		// 设置光标不可见
		Toolkit defaultToolkit = Toolkit.getDefaultToolkit();
		Image image = defaultToolkit.createImage(new MemoryImageSource(0, 0, null, 0, 0));
		Cursor invisibleCursor = defaultToolkit.createCustomCursor(image, new Point(0, 0), "cursor");
		setCursor(invisibleCursor);
		// ESC键退出
		KeyPressListener keyPressListener = new KeyPressListener();
		this.addKeyListener(keyPressListener);
		// this.setAlwaysOnTop(true);
		// 去标题栏
		this.setUndecorated(true);
		// 全屏
		this.getGraphicsConfiguration().getDevice().setFullScreenWindow(this);
		this.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
		setVisible(true);

		screenSize = Toolkit.getDefaultToolkit().getScreenSize();
		lines = screenSize.height / gap;
		columns = screenSize.width / gap;

		posArr = new int[columns + 1];
		random = new Random();
		for (int i = 0; i < posArr.length; i++) {
			posArr[i] = random.nextInt(lines);
		}

		// 每秒10帧
		new Timer(100, this).start();
	}

	@Override
	public void actionPerformed(ActionEvent e) {
		graphicsPanel.repaint();
	}

	private class GraphicsPanel extends JPanel {
		@Override
		public void paint(Graphics g) {
			Graphics2D g2d = (Graphics2D) g;
			g2d.setFont(getFont().deriveFont(Font.BOLD));
			g2d.setColor(Color.BLACK);
			g2d.fillRect(0, 0, screenSize.width, screenSize.height);
			// 当前列
			int currentColumn = 0;
			for (int x = 0; x < screenSize.width; x += gap) {
				int endPos = posArr[currentColumn];
				g2d.setColor(Color.CYAN);
				g2d.drawString(String.valueOf(getChr()), x, endPos * gap);
				int cg = 0;
				for (int j = endPos - 15; j < endPos; j++) {
					// 颜色渐变
					cg += 20;
					if (cg > 255) {
						cg = 255;
					}
					g2d.setColor(new Color(0, cg, 0));
					g2d.drawString(String.valueOf(getChr()), x, j * gap);
				}
				// 每放完一帧,当前列上雨点的位置随机下移1-5行
				posArr[currentColumn] += random.nextInt(5);
				// 当雨点位置超过屏幕高度时,重新产生一个随机位置
				if (posArr[currentColumn] * gap > getHeight()) {
					posArr[currentColumn] = random.nextInt(lines);
				}
				currentColumn++;
			}
		}
	}

	private class KeyPressListener extends KeyAdapter {
		@Override
		public void keyPressed(KeyEvent e) {
			if (e.getKeyCode() == KeyEvent.VK_ESCAPE) {
				System.exit(0);
			}
		}
	}

	/**
	 * @return 随机字符
	 */
	private char getChr() {
		return (char) (random.nextInt(94) + 33);
	}

	public static void main(String[] args) {
		new Rain();
	}

}